[BAO01-P09] Analysis of DNA damage in the radiation resistant microbe Deinococcus radiodurans R1 exposed to space in Tanpopo mission
Keywords:Panspermia hypothesis, Space exposure experiments, Cell aggregate, DNA damage, Tanpopo mission, Quantitative-PCR
Dried deinococcal cell-aggregates with different thickness were exposed to space (space samples) for about one year (space samples). The cells were also stored in the ground laboratory (ground references) and in ISS cabin (ISS references). After exposure or storage, genomic DNA was extracted from each sample and an 887-bp region in the rpoB gene was amplified by q-PCR. Intact DNA (%) was determined from the quotient N/N0, where N = copy number of rpoB gene amplified from DNA of exposed or stored cells and N0 = copy number of rpoB gene amplified from freshly prepared DNA.
Results and Discussion
Intact DNA (%) of the cell-aggregates with 100 µm-thickness exposed to space was less than 1% and all cells were dead. Pyrimidine dimer was major DNA damage caused by UV. On the other hand, DNA damage in those with 1000 μm-thickness was similar between the ground references and the space samples (Fig. 1). The result indicates that UV affected only the surface of the cell-aggregates. Intact DNA (%) in the ground references and the space samples (UV> 170 nm) with 500 μm-thickness were about 54%, and that in space samples (UV> 120 nm) with 500 μm-thickness was 46%. Although a significant difference is not recognized between the two samples, UV with shorter wavelength tended to induce more damage in DNA. Intact DNA (%) showed a good correlation with surviving fraction. We will also report the types and degrees of DNA damage using other methods.
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